The present invention relates generally to sensor assemblies and, more specifically, to modular sensor assemblies and methods of fabricating modular sensor assemblies.
Sensor assemblies are typically employed in applications including non-destructive evaluation (NDE) and medical diagnostic imaging, such as ultrasound applications and computed tomography (CT). The sensor assembly generally includes an array of sensors coupled to an electronics array. The sensor array generally includes hundreds or thousands of individual sensors. Similarly, the electronics array includes hundreds or thousands of integrated interface circuits (or “cells”) which are electrically coupled to provide electrical control of the sensors for beam forming, signal amplification, control functions, signal processing, etc.
One particular type of widely used sensor is the ultrasonic transducer. Two widely known types of ultrasonic transducers are capacitive micromachined ultrasonic transducers (cMUTs) and piezoelectric transducers (PZT). PZT sensors generally include a piezoelectric ceramic capable of producing electricity when subjected to mechanical stress. cMUT transducers are typically fabricated by forming a flexible membrane disposed over a cavity formed in the silicon substrate. By applying an electrode to the membrane, and to the base of the cavity in the silicon substrate, and applying appropriate voltages across the electrodes, the cMUT may be energized to produce ultrasonic waves. Similarly, when appropriately biased, the membrane of the cMUT may be used to receive ultrasonic signals by capturing reflected ultrasonic energy and transforming the energy into movement of the electrically biased membrane to generate a signal.
Fabricating the sensor array and the electronics array, and coupling the two arrays together, provides a number of design challenges. Semiconductor based sensors are generally fabricated in wafer form and diced, providing a number of sensor chips. PZT sensors are generally fabricated by dicing ceramic block material. Often PZT sensors are formed out of layers of ceramic, matching materials and damping materials. Each sensor sub-array typically includes many sensors. Each sensor sub-array or chip in the sensor array is typically coupled to an integrated circuit chip to provide individual control of each sensor. With hundreds or thousands of sensors and chips, each having countless electrical connections, the fabrication and assembly of such sensor assemblies can be challenging. This challenge becomes amplified when the application calls for size reduction in the sensor assembly. For sensor assemblies that are designed to be used inside the human body, or on small surfaces on the outside of the human body, it is generally desirable to reduce the overall size of the sensor assembly.
One way of reducing the size of the sensor assembly is to place the sensor array on top of the electronics array to provide greater packaging efficiency. However, stacking the sensor array on top of the electronics array introduces a wide variety of design challenges. Further, design, manufacturing and reliability concerns arise when considering the manufacturability of the sensor array, the formation of the sensor assembly, as well as providing a mechanism to cleanly route signals into and out of the sensor assembly.
Embodiments of the present invention may be directed to one or more of the challenges described above.